The present invention generally relates to packaging and more particularly is directed to a rotating stretch wrapping apparatus and process for making unitary packages which completely enclose loads.
Case packing or boxing is a common way of shipping products. These products are generally stacked in a corrugated box or are wrapped with kraft paper with the ends of the kraft paper being glued or taped.
However, customer dissatisfaction with gluing is high because removal of glued cartons or bags from the unitized loads tends to tear outside layers of the cartons or product. Glue further demands interleaving for product orientation requiring more durable and expensive packaging material.
Some manufacturers use steel or plastic strapping to unitize the product. The problems incurred in the use of strapping are the requirement of costly corner protectors, danger of bending or snapping and injuring the operator while applying the high tension strapping material to the loads, settling due to moisture wetting the cartons, and the sides bulging or normal vibrations causing the straps to loosen and the load to come apart.
In another packaging alternative, tape is used to horizontally bind the top layer of stacked loads. However, tape is expensive and allows relatively free movement of all product surrounded.
Another way of packaging products is by putting a sleeve or covering of heat shrinkable material around the products and shrinking the sleeve to form a unitized package. The use of heat shrinkable film is described in U.S. Pat. Nos. 3,793,798; 3,626,645; 3,590,549 and 3,514,920. A discussion of this art is set forth in U.S. Pat. No. 3,867,806.
The fastest growing and one of the most economical ways of packaging products is by wrapping the product load with a web of stretched plastic film.
The elasticity of the stretched plastic film holds the products of the load under more tension than either shrink wrap or kraft wrap, particularly with products which settle when packaged. The effectiveness of stretched plastic film in holding a load together is a function of the containment or stretch force being placed on the load and the ultimate stretch of the total layered film wrap. These two functions are determined by the modulus or hardness of the film after stretch has occurred and the ultimate strength of the film after application. Containment force is currently achieved by maximizing elongation until just below a critical point where breaking of the film occurs.
The use of wrapping machinery to wrap stretched film around a load is well-known in the art. Four types of stretch wrapping apparatus are commonly used in the package industry and these types are generally described as spiral rotary machines, full web rotary machines, pass-through machines, and circular rotating machines.
A spiral machine is shown in U.S. Pat. No. 3,863,425 in which film is guided from a roll and wrapped around a cylindrical load in a spiral configuration. A carriage drives the film roll adjacent the surface of the load to deposit a spiral wrap around the load and returns in the opposite direction to deposit another spiral overwrap around the load.
In U.S. Pat. No. 3,788,199, tapes are spirally wound in such a manner that they overlap each other to provide suitable space therebetween when breatheability is required. In this disclosure, a heavy duty bag is prepared by spirally winding stretched tapes of synthetic resin in opposite directions, so that they intersect each other to form a plurality of superimposed cylindrical bodies which are bonded together to form a cylindrical network. The spirally wound inner and outer tapes of the superimposed cylindrical body intersect each other at a suitable angle, depending upon the application intended, the preferred embodiment having substantially equal longitudinal transfer strength. In this preferred embodiment, the tapes intersect each other at an angle of about 90.degree.. The angle defined by the tapes constituting the cylindrical network may be determined by varying the interrelationship between the travelling speed of the endless belts carrying the tape and the rotating speed of the bobbin holders, which rotate a plurality of tape bobbins to deposit the tape onto the moveable belt.
Spiral wrapping machines which are currently commercially available are manufactured by Lantech, Inc. under Model Nos. SVS-80, SVSM-80, STVS-80, STVSM-80 and SAHS-80.
A full web type of apparatus which wraps stretched film around a rotating load is disclosed in U.S. Pat. No. 3,876,806 assigned to Lantech, Inc. A similar full web apparatus using a tensioned cling film wrapped around a rotating load is shown by U.S. Pat. No. 3,986,611 while another apparatus using a tacky PVC film is disclosed in U.S. Pat. No. 3,795,086.
Full web wrapping machines typical of those presently commercially available are Model Nos. S-65, T-65 and SAH-70 manufactured by Lantech, Inc.
Another type of machine for wrapping a pallet load commonly called a pass-through machine is disclosed in U.S. Pat. No. 3,596,434. In this patent, a pallet load is transported along a conveyor and the leading face of the pallet load contacts a vertical curtain of film formed by the sealed leading edges of film webs dispensed by two rolls of film on opposite sides of the path of the pallet load. The pallet load continues to move along the conveyor, carrying with it the sealed film curtain until the two side faces of the pallet load as well as the front face are covered by film web. A pair of clamping jaws then close behind the pallet load, bringing the two film web portions trailing from the side faces of the pallet load into contact with one another behind the pallet. The jaws then seal the film web portions together along two vertical lines, and cut the web portions between those two seals. Thus, the film web portions are connected to cover the trailing face of the pallet load, and the film curtain across the conveyor is re-established to receive the next pallet load. The pallet load may subsequently be exposed to heat in order to shrink the film web and apply unitizing tension to the load, as is disclosed in U.S. Pat. No. 3,662,512. Another disclosure of relevance to pass-through wrapping is U.S. Pat. No. 3,640,048 which shows that film may be applied to the top and bottom of the pallet load prior to the wrapping cycle when it is desired to cover all six surfaces of the pallet load with film. Commercial pass-through machines are currently manufactured by the Weldotron Corporation, Aktron Corporation, and SAT of France.
Various apparatus and processes have been developed to rotatably wrap stacked components to form a load.
Devices in which stationary loads are brought to a loading area and are wrapped by a rotating member which dispenses stretched film around a load are disclosed in U.S. Pat. Nos. 4,079,565 and 4,109,445. U.S. Pat. No. 4,079,565 discloses a full web vertical wrap of the load while U.S. Pat. No. 4,109,445 discloses the horizontal spiral wrap of a load. U.S. Pat. No. 4,050,220 issued to the inventors of the present invention discloses a wrapping device for multiple unit loads. Each load is conveyed to a wrapping area in which a load is supported on one or more stationary planar surfaces. The leading edge of a roll of stretchable plastic wrapping material is held adjacent to the load, and the roll of material is rotated about the load and the supporting planar surfaces, wrapping the load and the supporting surfaces together. Plastic wrapping material is stretched during the wrapping operation so that the material is under tension when applied to the load. After the wrapping cycle is complete, the load is pushed past the ends of the supporting surfaces, and the wrapping material which covered the supporting surfaces collapses against the supported sides of the load. Further developments of this wrapping system by the inventors of the present invention are disclosed in U.S. Pat. Nos. 4,110,957 and 4,178,734.
U.S. Pat. No. 603,585 discloses a spiral wrapping device for enclosing individual newspapers in paper wrap for mailing purposes. Each newspaper is placed on a cylindrical core with a circumference approximately twice that of a newspaper, and each newspaper advances along the length of the core as the core is rotated. Wrapping paper is applied to the core at an angle and the wrapping paper between newspaper is severed as each newspaper reaches the end of the cylinder and is placed on a flat horizontal surface, thereby collapsing the wrapping paper against the underside of the newspaper previously pressed to the cylinder.
U.S. Pat. No. 1,417,591 discloses a wrapping machine for individual items such as boxes in which each such item is conveyed along the surface of a horizontal sheet of wrapping material. The edges of wrapping material on each side of an item are curled upward to meet one another atop the item to be wrapped thereby forming a tube around the item. The leading end of the tube is sealed and the trailing end of the tube is severed and then sealed to enclose the item. Another device which utilizes this system of wrapping is disclosed in U.S. Pat. No. 3,473,288.
In U.S. Pat. No. 2,575,467, a wrapper of cylindrical packages for material such as sausage is disclosed in which the package is rotated about its cylindrical axis as wrapping tape is applied at an angle to form a cylindrical wrap.
In U.S. Pat. No. 2,863,270, two cylindrical items of approximately equal diameter are abutted at their planar ends, and placed by hand in a cradle which exposes the complete circumference of the abutting ends. A roll of wrapping material is then driven by a hand crank mechanism to circulate around the circumference of the abutting ends, applying wrapping material thereto. When sealed together, the pair of cylindrical items are removed from the cradle by hand.
A spiral wrapping machine for long bundles or items such as filaments is disclosed in U.S. Pat. No. 3,000,167. As the bundle of filaments moves along its axis through the wrapping area, a ring circulates about the bundle carrying a roll of wrapping material which is applied to the bundle to form a spiral wrap pattern. Because the normal load of filaments or similar items is much longer than the wrapping area, it is not necessary to provide support for the bundle in the wrapping area and, therefore, no support structure is wrapped with the bundle.
Commercial circular rotating wrapping machines are presently manufactured by Lantech, Inc., under the trademark LANRINER and are provided with wrapping ring inner diameters of 36 inches, 54 inches,72 inches and 84 inches. In differentiating between the various circular rotating wrapping machines manufactured by Lantech, Inc., the manual model has the designation SR; the full web models have the designations SVR and SAVR; the multiple banding models have the designation SVBR and SAVBR; the spiral models have the designation SVSR and SAVSR and the continuous wrap or bundler models have the model designations SVCR and SAVCR.
In these commercial machines, the load is pushed onto support tongues or wrapping rails and the load and support tongues are wrapped by a rotating supply of film. The film is stretched as it is rotated from the dispenser and the stretched film wrap holds the load together under compressive forces and also engages the tongues or wrapping rails on which the load is supported. The load is then pushed off or carried off of the tongues by the following load or take off conveyor respectively with the attendant frictional forces which result from the film engaging the tongues. Such forces can cause disorientation of the load.
It is apparent that the friction forces increase as the width of the tongues increase. Furthermore, the friction forces also increase as the tongues approach the corners of the load. Thus, prior art devices have had to utilize wrapping rails or tongues which did not extend past the corners or side edges of the load and have also had to contend with the problems of load support. While narrower tongues are preferred to reduce friction forces, strength requirements generally are such that because the bottom of the product or total weight of the load is supported by tongues, the tongues are necessarily thicker and wider and increase the friction forces. In addition, removal of the wrapped load from the tongues has caused difficulties since the present way to remove wrapped packages has been to push the packages from behind.
Other problems which occur include film tearing on the tongues when the load is being pushed off of the tongues along with product abrasion. Thus, bolts of cloth can become indented, metal pieces scored and product dented or crushed by passage over the tongues.
In an effort to overcome these problems the wrapping machine shown in U.S. Pat. No. 4,317,322 was developed. This system utilizes a plurality of conveyors, stacked vertically, to carry a load through a wrapping area encircled by a rotating ring wrapping apparatus. A film roll shaft extends from one side of the ring parallel to the rotational axis of the ring and to the conveyors. Film web is dispensed from a roll on the shaft, and is stretched by stretching means adjacent the shaft. The stretched tensioned web is wrapped about the load and the conveyors beneath the load. The bottom surface of the lower conveyor is driven at the same speed and in the same direction as the top surface of the upper load-carrying conveyor, so that the web wrapped around the load and conveyors is transported forward without drag. Beyond the wrapping area, a gap separates the conveyors from a subsequent takeoff conveyor, so that the tensioned web transported by the lower conveyor collapses against the underside of the load as the gap is encountered.
A swinging clamp arm is provided to clamp and cut film web at the end of each load. The clamp arm is driven in an arc to encounter the web between the roll and the load. Jaws mounted atop the clamp arm close on the web, and a cutting edge is then driven perpendicular to its length to sever the web between the jaws and the load. A brush atop the cutting edge brushes the web against underlying layers thereof to achieve a wrap seal based on web self-tackiness.
Spiral wrapping systems have previously failed to provide a satisfactory wrap to cover the leading and trailing ends of the load. Thus, where a load required end covering for protection or stability, it would have to be wrapped continually with film web being wrapped between loads to form a continuous casing. This method wastes film and, when the loads are separated by cutting the film wrap between the loads, provides only a loose covering which may snag and tear, causing a zippering of the entire wrap.
Another method utilized to provide end coverings is the manual draping of untensioned web around each end face prior to wrapping. This provides only a loose covering and requires careful attention to tucking of the draped portions during the wrapping process.